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Structure and mechanical properties of aluminosilicate geopolymer composites with Portland cement and its constituent minerals / Jonathan Tailby in Cement and concrete research, Vol. 40 N° 5 (Mai 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 787–794 Titre : Structure and mechanical properties of aluminosilicate geopolymer composites with Portland cement and its constituent minerals Type de document : texte imprimé Auteurs : Jonathan Tailby, Auteur Année de publication : 2012 Article en page(s) : pp. 787–794 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Composites  ;  Mechanical  properties  ;  Microstructure  ;NMR Résumé : The compressive strengths and structures of composites of aluminosilicate geopolymer with the synthetic cement minerals C3S, β-C2S, C3A and commercial OPC were investigated. All the composites showed lower strengths than the geopolymer and OPC paste alone. X-ray diffraction, 29Si and 27Al MAS NMR and SEM/EDS observations indicate that hydration of the cement minerals and OPC is hindered in the presence of geopolymer, even though sufficient water was present in the mix for hydration to occur. In the absence of SEM evidence for the formation of an impervious layer around the cement mineral grains, the poor strength development is suggested to be due to the retarded development of C–S–H because of the preferential removal from the system of available Si because geopolymer formation is more rapid than the hydration of the cement minerals. This possibility is supported by experiments in which the rate of geopolymer formation is retarded by the substitution of potassium for sodium, by the reduction of the alkali content of the geopolymer paste or by the addition of borate. In all these cases the strength of the OPC–geopolymer composite was increased, particularly by the combination of the borate additive with the potassium geopolymer, producing an OPC–geopolymer composite stronger than hydrated OPC paste alone. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003494 [article] Structure and mechanical properties of aluminosilicate geopolymer composites with Portland cement and its constituent minerals [texte imprimé] / Jonathan Tailby, Auteur . - 2012 . - pp. 787–794. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 5 (Mai 2010) . - pp. 787–794 Mots-clés : Composites  ;  Mechanical  properties  ;  Microstructure  ;NMR Résumé : The compressive strengths and structures of composites of aluminosilicate geopolymer with the synthetic cement minerals C3S, β-C2S, C3A and commercial OPC were investigated. All the composites showed lower strengths than the geopolymer and OPC paste alone. X-ray diffraction, 29Si and 27Al MAS NMR and SEM/EDS observations indicate that hydration of the cement minerals and OPC is hindered in the presence of geopolymer, even though sufficient water was present in the mix for hydration to occur. In the absence of SEM evidence for the formation of an impervious layer around the cement mineral grains, the poor strength development is suggested to be due to the retarded development of C–S–H because of the preferential removal from the system of available Si because geopolymer formation is more rapid than the hydration of the cement minerals. This possibility is supported by experiments in which the rate of geopolymer formation is retarded by the substitution of potassium for sodium, by the reduction of the alkali content of the geopolymer paste or by the addition of borate. In all these cases the strength of the OPC–geopolymer composite was increased, particularly by the combination of the borate additive with the potassium geopolymer, producing an OPC–geopolymer composite stronger than hydrated OPC paste alone. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003494